Boron Operations is a world-class borate mine located in the western Mojave Desert of California. The climate is classified as harsh, with an evaporation to precipitation ratio of nearly 25:1.
Overburden slopes are piles of waste soil created as part of the mining process. They consist mainly of silty arkosic sandstone soils which contain varying levels of residual boron. The threat of boron-related soil toxicity on native plant re-establishment is widespread and we believe unique to this mine.
The research helped determine the right mix of native seeds for reclamation of the slopes.
Overburden slope reclamation began in 1995 and continues today. This process involves sampling the mine overburden prior to stripping. The final slopes are contour-tilled and seeded with a native mix whose species were selected based on the test plots and early slope results.
During March and April 2015, we collected data on vegetative cover, species richness, and plant density from the overburden final slopes seeded between 1995 and 2008. Data was required to determine which slopes had met the ten-year minimum success criteria for reclamation, as stipulated in the agency-approved Boron mine 2008 reclamation plan and the California Surface Mining and Reclamation Act of 1975.
The data was compared with vegetation samples taken from the overburden expansion area in 1994, prior to disturbance. Of the 230 acres sampled, a total of 207.55 acres met the success criteria and were subsequently designated as reclaimed by the California Department of Conservation’s Office of Mine Reclamation.
This reclamation programme’s success is unprecedented in California, and will be used as a template for the ongoing reclamation of overburden slope and ultimately site closure. The programme can also be applied to other reclamation efforts in the Mojave Desert.